Health Risks of Cannabis Use

Knowledge about cannabis and its impacts is constantly evolving. The majority of people who use cannabis do not suffer any negative consequences. However, various factors seem to contribute to negative effects in some people.

Risk factors

Although problems may occur for first-time cannabis users, issues related to physical and mental health mainly arise as a result of repeated use over several months or years. Accidents and injuries, on the other hand, may occur as a result of one-time or occasional use. Certain factors can increase or reduce a cannabis user’s risk of being negatively affected:

  • A personal or family history of mental health issues such as psychosis and bipolar disorder
  • Frequency of use: Regular use (once a week or more) is often linked to increased risk of health problems
  • Type of product used: Products with higher THC content may be more harmful
  • The age at which a person starts to use cannabis: use during adolescence is generally associated with an increased risk of negative effects
  • The circumstances of use, for example:
    • When cannabis is combined with other substances such as alcohol or medications 
    • When an individual has personal responsibilities such as work or the supervision of children
  • The method of use: Smoking cannabis appears to be more risky than other methods of use, although poisoning from foods containing cannabis is common among inexperienced users.

However, caution should be exercised before attributing the cause of a health problem to cannabis use. It is possible that the problem:

  • Was already present prior to cannabis use
  • Is a result of cannabis use
  • Is influenced by cannabis use or, conversely, influences cannabis use

Based on these factors, it is difficult to predict whether or not an individual will experience significant problems after using cannabis. Most experts agree that cannabis use is never 100% safe.

Risks to cognitive abilities

The health risks and negative health impacts of cannabis use stem from its effects on cognitive abilities, such as:  

  • Judgement 
  • Attention span
  • Memory
  • The ability to make decisions

These effects can impact daily activities such as:

  • Driving a car
  • Work
  • Learning activities 
  • Other situations that require coordination and speed 

Cannabis begins to take effect within minutes of being inhaled, and a little later if ingested. The effects often last for several hours and are usually reversible. Some studies suggest that reduced cognitive function may persist longer in the event of sustained and repeated use, especially if it begins in adolescence.

Physical health risks

Cannabis use can exacerbate some existing health problems, such as chronic diseases:

  • Cannabis use increases the heart rate and can alter its rhythm. It also increases blood pressure.
  • Inhaling cannabis smoke can aggravate existing respiratory diseases and even promote disease onset.
  • Like tobacco smoke, cannabis smoke contains a number of substances that are harmful to your health, including some carcinogens. 
  • However, the most recent scientific studies do not prove that the risk of developing lung, throat, or neck cancer is higher among cannabis users.

Mental health risks

Psychotic symptoms

Individuals who are under the influence of cannabis may experience psychotic symptoms such as: 

  • Hallucinations with false visual, auditory, and/or tactile perceptions
  • Paranoid ideas that seem detached from reality 

In most cases, these psychotic experiences are limited to when the person is intoxicated and disappear on their own. Other individuals may experience persistent, long-term, and much more serious symptoms. According to experts, cannabis use does not cause psychotic disorders, but it can be a contributing factor for some people.


Individuals who regularly use cannabis may show a lack of interest in activities other than using cannabis (studies, work, leisure, etc.). They may also experience symptoms of depression, for example:  

  • Deep sadness
  • Fatigue
  • Irritability
  • Sense of worthlessness

Some individuals with depression may be tempted to use cannabis to relieve their symptoms. To date, scientific evidence has not shown that cannabis is effective in treating depression. Using it for this purpose is not recommended.


Some studies suggest that cannabis users experience symptoms of anxiety more frequently than non-users However, it is difficult to predict whether or not cannabis will influence their anxiety levels. Some people may experience panic attacks when they use cannabis, while others find it relaxing. 

Problematic cannabis use

Cannabis use can be problematic if people lose control of their use and suffer negative consequences in various spheres of their life as a result. Some people may become addicted to cannabis, as it is the case with other substances. Individuals may:

  • Develop a tolerance to the substance (i.e., need to use more to feel the same effect)
  • Experience withdrawal symptoms when they reduce or stop use
  • Have a strong desire to use
  • Be unable to stop using
  • Spend a significant portion of their time buying or using cannabis or recovering from cannabis use
  • Use repeatedly in such a way that it prevents them from fulfilling important obligations at work, school, or home 
  • Use despite personal and/or social problems related to use 
  • Reduce or give up social, professional, or leisure activities as a result of use 

About 1 in 11 people who use cannabis will develop a problematic use of cannabis in their lifetime. Among adolescents, 1 in 6 users will develop addiction problematic use. Use of and addiction to other products including alcohol and tobacco are more common among cannabis users. 

Research has also established the existence of a cannabis withdrawal syndrome. It occurs when regular cannabis users significantly reduce or stop cannabis use. Symptoms include: 

  • Restlessness 
  • Irritability
  • Sleep problems, which may last a number of weeks after stopping use

Risks for pregnant women

Using cannabis during pregnancy could have negative effects on the unborn child. There is some evidence to suggest that cannabis may affect childhood growth and cognitive development. In some cases, the effects may only appear in adolescence.  There is currently no known safe threshold for cannabis use during pregnancy. Based on the scientific data, pregnant women should avoid using cannabis. 

For more information, visit the Alcohol or Other Drug Use During Pregnancy and Breastfeeding page on the Portail Santé mieux-être.

Last update: March 21, 2018 3:40 PM